1. Field of the Invention
The present invention relates to a method of joining together magnetic and nonmagnetic materials, namely a magnetic material such as carbon steel for machine construction and a nonmagnetic material such as stainless steel or aluminum.
2. Description of the Prior Art
Such a magnetic and a nonmagnetic material are both metals, and for joining such dissimilar metals together, techniques has so far been known including a mechanical joining method, e.g., press fitting or calking, and also brazing, adhesive bonding, spot welding, friction welding and electron-beam welding methods.
Of these prior-art techniques, the mechanical joining methods present a problem of deformation during joining and are also hard to ensure sealing. The brazing method offers only a limited bonding strength and, relying on partial heating along a joining line, entails the problem that deformation is produced by the partial heating. The adhesive bonding method gives rise to problems in bonding strength and reliability of joining. In the methods such as spot welding, friction welding and electron-beam welding that require fusion to join, not only is the problem encountered that a brittle intermetallic compound formed at a weld prevents joining with reliability, but also it becomes the problem that depending on temperatures at which the weld is heated and cooled and time durations in which it is then held, respectively, its metallographic structure may be caused to change adversely so that the weld is cracked or becomes brittle. Especially in the electron-beam welding process, the problem of deformation by heating as in the brazing process is left unresolved together with the problem that excess weld metal portions must be cut for removal.